CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > OpenFOAM > OpenFOAM Community Contributions

[waves2Foam] Trying to implement relaxation zones in waveDyMFoam

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   February 28, 2017, 09:38
Default Trying to implement relaxation zones in waveDyMFoam
  #1
Member
 
Gautami Erukulla
Join Date: Mar 2009
Posts: 71
Rep Power: 14
gautami is on a distinguished road
Dear Dr. Jacobsen,

Simulation of a 2D wave tank with a floating object case using waveDyMFoam.

The details are:

wave tank length 13 m (500 cells) , wave tank height 2 m (100 cells). Total 50000 cells.

The simulation was completed in 12 hours for an endTime of 35s.

To have an idea of relaxing.correct() on the simulation time, I made a change to waveDyMFoam.C code by not incluidng “relaxing.correct()” in the code. Then I recompiled waveDyMfoam and simulated the same case. The simulation was completed in 4 hours. As we would expect the results show no wave relaxation at the relaxation zones.

Kindly can you please let me know the inclusion of “relaxing.correct()” in waveDyMFoam.C can increase the simulation time by a factor of 3. Please find attached the case file (testCasesb.tar.gz) and details of the case and the waveDyFoam.C codes (waveDyMFoamsb.pdf). Kindly please let me know if I am doing something wrong.

3D simulation case: 3D wave tank with a fixed truncated vertical cylinder, with a mesh size of 2 million cells and a max Courant number 0.25 was completed in 1 day 13 hours for an endTime of 25s using waveFoam solver (parallel run on 24 cores).
The same 3D simulation case with 2 million cells, providing 3 degree of freedom (surge,heave and pitch) to the cylinder using waveDyFoam solver is getting computationally very expensive. A parallel run on 36 cores is taking 1 day and 12 hours to simulates until 2 secs.

Your insights on this will be highly invaluable.Please do let me know if I need to provide any additional information. Sorry for any trouble caused. Thank you for your time and consideration.

Most&More,
Gautami Erukulla
Attached Files
File Type: pdf waveDyMFoamsb.pdf (88.0 KB, 41 views)
File Type: gz testCasesb.tar.gz (7.4 KB, 26 views)
gautami is offline   Reply With Quote

Old   February 28, 2017, 12:49
Default
  #2
ngj
Senior Member
 
Niels Gjoel Jacobsen
Join Date: Mar 2009
Location: Deltares, Delft, The Netherlands
Posts: 1,872
Rep Power: 34
ngj will become famous soon enoughngj will become famous soon enough
Hi Gautami,

Thank you for the comments, I am not certain, but I can try to answer your question (btw, you do not need to recompile to remove relaxation zones. Simply do not define them in relaxationZoneNames).

What you experience is likely due to the fact that you reevaluate the relaxation zone every time, or more precisely: You find all the cells in the zone again every time step. Try to use the 'frozen' type of zone. This allows for a static set of cell indices. Note, however, that this only works for topologically static meshes, i.e. deformation is allowed, but not a change in number of cells.

Please let me know, whether this helps.

Kind regards

Niels
__________________
Please note that I do not use the Friend-feature, so do not be offended, if I do not accept a request.
ngj is offline   Reply With Quote

Old   February 28, 2017, 15:42
Default
  #3
Member
 
Gautami Erukulla
Join Date: Mar 2009
Posts: 71
Rep Power: 14
gautami is on a distinguished road
Dear Dr. Jacobsen,

Thank you very much for your advise. Will work on it and will keep you posted.
Thanks again!

Most&More,
Gautami Erukulla.
gautami is offline   Reply With Quote

Old   March 2, 2017, 08:27
Default
  #4
Member
 
Gautami Erukulla
Join Date: Mar 2009
Posts: 71
Rep Power: 14
gautami is on a distinguished road
Dear Dr. Jacobsen,

As per your advise, I simulated the 2D wave tank with a floating object case (50000 cells), using Frozen relaxation. (version OpenFoam 2.3.0)
The frozen relaxation zone is defined as:

At Inlet:

relaxationZone
{
relaxationScheme Spatial;

relaxationShape Frozen;
actualRelaxationShape Rectangular;

beachType Empty;

relaxType INLET;
startX (0 0.0 -1);
endX (4 0.0 1);
orientation (1.0 0.0 0.0);
}

At outlet:


relaxationZone
{
relaxationScheme Spatial;

relaxationShape Frozen;
actualRelaxationShape Rectangular;

beachType Empty;
relaxType OUTLET;
startX (9 0.0 -1);
endX (13 0.0 1);
orientation (1.0 0.0 0.0);
}

The simulation took the same amount of time 12.8 hours for and endTime of 35s. I am not sure if I am defining the frozen relaxation zone in the correct way. I also tried to define the frozen relaxation zone as:

At inlet:

relaxationZone
{
relaxationScheme Spatial;
relaxationType Frozen;
relaxationShape Rectangular;
beachType Empty;

relaxType INLET;
startX (0 0.0 -1);
endX (4 0.0 1);
orientation (1.0 0.0 0.0);
}

At outlet:

relaxationZone
{
relaxationScheme Spatial;

relaxationType frozen;
relaxationShape Rectangular;
beachType Empty;

relaxType OUTLET;
startX (9 0.0 -1);
endX (13 0.0 1);
orientation (1.0 0.0 0.0);
}

There was no difference in the time (it took 12.8 hours for and endTime of 35s). I am making a mistake in defining the frozen zones. Kindly can you please help me in defining the frozen relaxation zone the right way. Thank you very much for your consideration.

Most&More,
Gautami Erukulla.
gautami is offline   Reply With Quote

Old   March 3, 2017, 10:10
Default
  #5
Member
 
Gautami Erukulla
Join Date: Mar 2009
Posts: 71
Rep Power: 14
gautami is on a distinguished road
Dear Dr. Jacobsen,

This is in regard to my earlier message about frozen relaxation zone. I had defined the frozen relaxation zone as:

AT INLET :
relaxationZone
{
relaxationScheme Spatial;
actualRelaxationShape Rectangular;
relaxationShape Frozen;
beachType Empty;
relaxType INLET;
startX (0 0.0 -1);
endX (4 0.0 1);
orientation (1.0 0.0 0.0);
}

AT OUTLET
relaxationZone
{
relaxationScheme Spatial;
actualRelaxationShape Rectangular;
relaxationShape Frozen;
beachType Empty;

relaxType OUTLET;
startX (9 0.0 -1);
endX (13 0.0 1);
orientation (1.0 0.0 0.0);
}

Under the folder 'constant' the following four files are created:
cells_inlet, cells_outlet, sigma_inlet and sigma_outlet and these folders define the cells in the frozen relaxation zones (15400). I guess the frozen relaxation zone effect is being implemented during the simulation. However defining the frozen relaxation zone did not have any effect of expediting the simulation time.
3D simulation is getting computationally very expensive, with 2 million cells, Courant number 0.2, is taking 3 days to simulate to 2.5s and it looks it will take 25 days to complete the simulation for an endTime of 25s. I was wondering and hoping if there is any way to use the waveDyFoam solver with the relaxation zone, without increasing the computational time drastically.
I apologize for causing any trouble to you with this issue. Any guidance in this regards will be immensely helpful. Thank you

Most&More,
Gautami Erukulla.
gautami is offline   Reply With Quote

Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Lets talk about relaxation factor optimization chriss85 OpenFOAM Running, Solving & CFD 35 June 21, 2019 09:54
Building problems with cell zones when reopening Fluent MJ2017 FLUENT 0 October 14, 2017 08:11
About equation relaxation chriss85 OpenFOAM Running, Solving & CFD 1 May 2, 2017 19:52
Relaxation and convergence sammi Phoenics 0 March 20, 2008 03:32
Question on adjusting relaxation factor CFD Rookie Main CFD Forum 3 January 26, 2004 14:37


All times are GMT -4. The time now is 18:49.